Turkey's chances of hosting the 2020 Olympics have been dealt a serious blow with a widespread doping scandal. Dozens of athletes are expected to be confirmed as having tested positive for banned substances after the International Association of Athletics Federations "intensified" its anti-doping efforts within Turkey this year, with particular scrutiny at the Mediterranean Games last month. The spate of positive tests comes after "abnormalities" were recorded in the blood biological passport of the Olympic 1500m champion Cakir Alptekin, who may face a life ban from athletics after being suspended in May. Commenting on the Alptekin case in March this year, after the 27-year-old won gold at London 2012, an IAAF spokesman told the Guardian: "We have seen big abnormalities and it is not the only case from Turkey. More are coming." If the IAAF confirms the positive cases before the International Olympic Committee decides which city will host the 2020 Games in September, then it will be extremely damaging for Istanbul, which is vying with Tokyo and Madrid to stage the event. Another high-profile Turkish athlete who has tested positive for a banned substance is the two-times European 100m hurdle champion, Nevin Yanit.

However, despite eight Turkish athletes reportedly failing tests at last month's European Team Championships in Gateshead, the National Olympic Committee of Turkey insists there is a zero-tolerance approach to doping in the country and the new cases will be resolved "quickly and decisively".

A spokesman said: "The NOC of Turkey and the Turkish government have a zero-tolerance policy on doping in sport and therefore we have been cooperating fully with all relevant investigations to resolve these cases as quickly and decisively as possible.

"The recent doping discoveries have been fully assisted by the Turkish National Anti-doping Agency who have been working closely with the IAAF and World Anti-doping Agency. The Turkish Anti-Doping Agency is wholly compliant with Wada and is dramatically stepping up its fight against drug cheats.

"Any athletes found guilty of using banned substances will be punished to the full extent of Turkey's comprehensive anti-doping legislation, other laws, and

in accordance with international anti-doping practices."

It is unlikely that Turkey will be banned from competing at this year's world championships in Moscow, despite the high number of offences. No country has ever been suspended from a major event because of doping offences and the IAAF council, which has the power to make such a decision, does not sit until the eve of the championships in August, when Turkey's athletes will already be in Russia.

With only eight weeks remaining until the IOC makes a decision on the 2020 Olympics in Buenos Aires, Istanbul bid insiders insisted that Turkey's Olympic committee had been working hard with anti-doping agencies to uncover potential cheats.

When Alptekin won gold at last year's Olympics she claimed the result was down to "Turkish power", although the British athlete Lisa Dobriskey immediately raised suspicions when saying she felt "uncomfortable" at the result.

The IAAF would not confirm how many Turkish athletes are expected to be confirmed as positive but said in a statement: "Following concerns highlighted by abnormal biological passport values the IAAF with the national anti-doping agency intensified the testing programme in Turkey, the results of which remain on-going in accordance with IAAF Rules. The IAAF will not make any further comment until the completion of those proceedings."